What is a healthy BMI?

A BMI between 18.5 and 24.9 is considered normal weight. Below 18.5 is underweight, 25–29.9 is overweight, and 30+ is obese according to WHO standards.

BMI is a useful screening tool but doesn't measure body fat directly. It can misclassify muscular athletes as overweight. Use it alongside waist circumference and other health markers.

Health Calculator

Your Body Mass Index, calculated instantly

Enter your height and weight to see your BMI, health category, ideal weight range, and body fat estimate. Supports metric and imperial units.

💡Your BMI is 24.2 — Normal weight

Used by 50,000+ users monthly · No sign-up required · Instant results

Your measurements

Sex

Age30 years

Height170 cm

Weight70 kg

Your BMI

24.2

Normal weight

BMI 18.5–25

BMI scale

1618.525303540+

Ideal weight range

53–72 kg

BMI 18.5–24.9

Body fat estimate

19.8%

Male, age 30

Weight to goal

Ideal ✓

You're in the healthy range

BMI categories (WHO)

Severely underweight0–16

Underweight16–18.5

Normal weight18.5–25

Overweight25–30

Obese class I30–35

Obese class II35–40

Obese class III40–+

💡 BMI is a screening tool, not a complete health picture. For a more accurate assessment, combine it with your body fat percentage (which accounts for muscle mass) and your daily calorie needs (TDEE) to build a complete fitness picture.

How to calculate BMI

Body Mass Index is calculated by dividing your weight in kilograms by the square of your height in metres:

BMI = kg ÷ m²

Example: Someone who is 170cm (1.70m) and weighs 70kg:
BMI = 70 ÷ (1.70)² = 70 ÷ 2.89 = 24.2

In imperial: BMI = (lbs × 703) ÷ inches². At 5'7" and 154lbs: (154 × 703) ÷ 67² = 24.1.

WHO BMI categories

Underweight< 18.5

Normal weight18.5 – 24.9

Overweight25.0 – 29.9

Obese Class I30.0 – 34.9

Obese Class II35.0 – 39.9

Obese Class III≥ 40.0

BMI limitations — what it doesn't measure

BMI is a useful population-level screening tool, but it has well-documented individual limitations that are important to understand before interpreting your result.

It doesn't distinguish fat from muscle

A professional athlete with 8% body fat may have a BMI of 28 (overweight) due to high muscle mass, while someone with a BMI of 24 (normal) may carry excess abdominal fat. For a more precise measure, use the body fat percentage calculator.

Fat distribution matters more than BMI

Abdominal (visceral) fat is more strongly associated with cardiovascular disease and type 2 diabetes than overall BMI. Waist circumference is a better predictor of metabolic risk: above 94cm for men and 80cm for women indicates elevated risk regardless of BMI.

Age and ethnicity differences

BMI thresholds were developed primarily from European populations. Research suggests that people of Asian descent face increased health risks at lower BMI thresholds — some health organisations recommend a BMI threshold of 23 (rather than 25) for overweight in Asian populations. Older adults also naturally carry more fat at the same BMI due to muscle loss.

BMI and healthy weight — what the research says

Minimum mortality

22–23

Studies show lowest all-cause mortality at BMI 22–23 in non-smokers

Cardiovascular risk increase

BMI 25+

Relative risk of heart disease begins rising above the normal range

Metabolic risk threshold

BMI 30+

Type 2 diabetes risk increases approximately 10× vs normal weight

The most comprehensive approach to health assessment combines BMI with waist circumference, body fat percentage, blood pressure, and blood glucose. If you're using BMI as a starting point, pair it with the calorie calculator to determine your daily energy needs for weight management.

Frequently asked questions

Body Mass Index (BMI) is a numerical measure that uses your height and weight to estimate whether you're at a healthy weight. The formula is: BMI = weight (kg) / height (m)². For example, someone who is 170cm and 70kg has a BMI of 70 / 1.7² = 24.2 — within the normal range. BMI is widely used in healthcare as an initial screening tool because it's simple, cheap, and consistent. It was developed in the 1830s by Belgian statistician Adolphe Quetelet and later adopted by the World Health Organisation. While imperfect, it remains the most commonly used population-level health metric.

The WHO defines BMI categories as follows: Under 18.5 is underweight; 18.5–24.9 is normal weight; 25.0–29.9 is overweight; and 30.0 or above is obese. These ranges apply to adults (18+) of all ages and are the same for both men and women. The healthy BMI range (18.5–24.9) corresponds to the lowest risk of weight-related health conditions like type 2 diabetes, cardiovascular disease, and certain cancers. Some health authorities, particularly in Asian countries, use lower thresholds (23+ for overweight) because research shows health risks increase at lower BMIs in these populations.

BMI is a useful starting point but has significant limitations. It doesn't measure body fat directly — it's a weight-to-height ratio. As a result, muscular athletes can have a high BMI despite low body fat, while elderly people can have a normal BMI but high body fat due to muscle loss (called "normal weight obesity"). BMI also doesn't account for where fat is distributed. Abdominal fat (waist circumference over 94cm for men or 80cm for women) is more strongly associated with metabolic risk than total body fat. For a more complete picture, combine BMI with waist measurement, body fat percentage, blood pressure, and blood markers. Use our body fat calculator alongside BMI for a better assessment.

The ideal weight range for a given height corresponds to the BMI range of 18.5–24.9. For someone 170cm tall, that's 53.5–72kg. For 180cm, it's 60–80.7kg. This calculator shows your specific ideal range in real time. However, "ideal weight" is not a single number. Factors like muscle mass, bone density, age, and ethnicity all affect what's healthy for a given individual. A fit, muscular person at the upper end of the healthy BMI range may be healthier than a sedentary person in the middle of it. Use the ideal weight range as a guide, not a rigid target.

BMI is most useful as a trend indicator rather than an absolute number. If you're working on weight loss or gain, tracking BMI over time (monthly) helps you see whether your efforts are having effect at a population-health level. Pair BMI with more sensitive measurements: body fat percentage (our body fat calculator), photos, how your clothes fit, energy levels, and fitness metrics like how far you can run or how much you can lift. These give a fuller picture of your health progress than BMI alone. The Australian Government's healthdirect.gov.au also has resources on healthy weight management tailored to Australians.

Related calculators

Percentage Calculator